About Parameters
Short description
Describes how to work with command parameters in PowerShell.
Long description
Most PowerShell commands, such as cmdlets, functions, and scripts, rely on parameters to allow users to select options or provide input. The parameters follow the command name and have the following form:
-<parameter_name> <parameter_value>
-<parameter_name>:<parameter_value>
The name of the parameter is preceded by a hyphen (-), which signals to PowerShell that the word following the hyphen is a parameter name. The parameter name and value can be separated by a space or a colon character. Some parameters do not require or accept a parameter value. Other parameters require a value, but do not require the parameter name in the command.
The type of parameters and the requirements for those parameters vary. To find
information about the parameters of a command, use the Get-Help cmdlet. For
example, to find information about the parameters of the Get-ChildItem cmdlet,
type:
Get-Help Get-ChildItem
To find information about the parameters of a script, use the full path to the script file. For example:
Get-Help $home\Documents\Scripts\Get-Function.ps1
The Get-Help cmdlet returns various details about the command, including a
description, the command syntax, information about the parameters, and
examples showing how to use the parameters in a command.
You can also use the Parameter parameter of the Get-Help cmdlet to find
information about a particular parameter. Or, you can use the Parameter
parameter with the wildcard character ( * ) value to find information about
all parameters of the command. For example, the following command gets
information about all parameters of the Get-Member cmdlet:
Get-Help Get-Member -Parameter *
Default parameter values
Optional parameters have a default value, which is the value that is used or assumed when the parameter is not specified in the command.
For example, the default value of the ComputerName parameter of many cmdlets is the name of the local computer. As a result, the local computer name is used in the command unless the ComputerName parameter is specified.
To find the default parameter value, see help topic for the cmdlet. The parameter description should include the default value.
You can also set a custom default value for any parameter of a cmdlet or advanced function. For information about setting custom default values, see about_Parameters_Default_Values.
Parameter attribute table
When you use the Full, Parameter, or Online parameters of the
Get-Help cmdlet, Get-Help displays a parameter attribute table with
detailed information about the parameter.
This information includes the details you need to know to use the parameter.
For example, the help topic for the Get-ChildItem cmdlet includes the
following details about its Path parameter:
-path <string[]>
Specifies a path of one or more locations. Wildcard characters are
permitted. The default location is the current directory (.).
Required? false
Position? 0
Default value Current directory
Accept pipeline input? true (ByValue, ByPropertyName)
Accept wildcard characters? true
The parameter information includes the parameter syntax, a description of the parameter, and the parameter attributes. The following sections describe the parameter attributes.
Parameter Required
This setting indicates whether the parameter is mandatory, that is, whether all commands that use this cmdlet must include this parameter. When the value is True and the parameter is missing from the command, PowerShell prompts you for a value for the parameter.
Parameter Position
If the Position setting is set to a positive integer, the parameter name is
not required. This type of parameter is referred to as a positional parameter,
and the number indicates the position in which the parameter must appear in
relation to other positional parameters. A named parameter can be listed in any
position after the cmdlet name. If you include the parameter name for a
positional parameter, the parameter can be listed in any position after the
cmdlet name.
For example, the Get-ChildItem cmdlet has Path and Exclude parameters. The
Position setting for Path is 0, which means that it is a positional
parameter. The Position setting for Exclude is named.
This means that Path does not require the parameter name, but its parameter value must be the first or only unnamed parameter value in the command. However, because the Exclude parameter is a named parameter, you can place it in any position in the command.
As a result of the Position settings for these two parameters, you can use
any of the following commands:
Get-ChildItem -Path c:\techdocs -Exclude *.ppt
Get-ChildItem c:\techdocs -Exclude *.ppt
Get-ChildItem -Exclude *.ppt -Path c:\techdocs
Get-ChildItem -Exclude *.ppt c:\techdocs
If you were to include another positional parameter without including the
parameter name, that parameter must be placed in the order specified by the
Position setting.
Parameter Type
This setting specifies the Microsoft .NET Framework type of the parameter value. For example, if the type is Int32, the parameter value must be an integer. If the type is string, the parameter value must be a character string. If the string contains spaces, the value must be enclosed in quotation marks, or the spaces must be preceded by the escape character ( ` ).
Default Value
This setting specifies the value that the parameter will assume if no other value is provided. For example, the default value of the Path parameter is often the current directory. Required parameters never have a default value. For many optional parameters, there is no default because the parameter has no effect if it is not used.
Accepts Multiple Values
This setting indicates whether a parameter accepts multiple parameter values. When a parameter accepts multiple values, you can type a comma-separated list as the value of the parameter in the command, or save a comma-separated list (an array) in a variable, and then specify the variable as the parameter value.
For example, the ServiceName parameter of the Get-Service cmdlet accepts
multiple values. The following commands are both valid:
Get-Service -servicename winrm, netlogon
$s = "winrm", "netlogon"
Get-Service -servicename $s
Accepts Pipeline Input
This setting indicates whether you can use the pipeline operator ( | ) to
send a value to the parameter.
Value Description
----- -----------
False Indicates that you cannot pipe a value to the
parameter.
True (by Value) Indicates that you can pipe any value to the
parameter, just so the value has the .NET
Framework type specified for the parameter or the
value can be converted to the specified .NET
Framework type.
When a parameter is "True (by Value)", PowerShell tries to associate any piped values with that parameter before it tries other methods to interpret the command.
True (by Property Name) Indicates that you can pipe a value to the
parameter, but the .NET Framework type of the
parameter must include a property with the same
name as the parameter.
For example, you can pipe a value to a Name parameter only when the value has a property called Name.
Note
A typed parameter that accepts pipeline input (by Value) or
(by PropertyName) enables use of delay-bind script blocks on the parameter.
The delay-bind script block is run automatically during
ParameterBinding. The result is bound to the parameter. Delay binding
does not work for parameters defined as type ScriptBlock or
System.Object, the script block is passed through
without being invoked.
You can read about delay-bind script blocks here about_Script_Blocks.md
Accepts Wildcard Characters
This setting indicates whether the parameter's value can contain wildcard characters so that the parameter value can be matched to more than one existing item in the target container.
Common Parameters
Common parameters are parameters that you can use with any cmdlet. For more information about common parameters, see about_CommonParameters.